A large amount of the world's oil comprises heavy, viscous crude oil having an API gravity of less than about 15.degree.. With the gradual depletion of higher gravity, more easily produced crude oils, the recovery of these viscous, heavy crudes becomes increasingly important.
In order to produce such heavy, viscous crudes, several means have been developed for lowering the viscosity of the crude so that production by normal pumping equipment can be accomplished. One method involves the dilution of the viscous crude with a lighter, higher gravity crude or a hydrocarbon diluent such as kerosene distillate, or diesel fuel. Such dilution effectively raises the gravity of the heavy crude so that it may be economically produced by common oil field procedures. The main drawback of this procedure is that valuable fluids must be pumped downhole in order to produce less valuable fluids. The economic break point of such a procedure is high.
Another method for producing heavy, viscous crude oil involves the heating of the crude oil in place in the formation to lower the viscosity of the oil. Injection of hot fluids such as steam and/or water or the actual burning of some of the oil in place has been utilized to accomplish such formation heating. Specialized equipment must be utilized for producing such oil since the viscosity will again increase if it is allowed to cool. Therefore, it is necessary to utilize specially constructed, insulated tubing in the well bore to retain as much heat as possible to allow high temperature production. The economic break-even point of such a system is also high because large amounts of energy must be consumed in the heating process.
Another method for producing heavy, viscous crude is through emulsification with water and surfactant downhole so that the oil can be produced as a low viscosity, oil-in-water emulsion. In such processes, a water and surfactant solution is admitted to the well bore where it mixes with the heavy, viscous crude within or adjacent to a downhole pump. The emulsion is then formed through the agitation and movement of the mixture induced by the reciprocating action of the downhole pump. U.S. Pat. Nos. 3,380,531 and 3,467,195 describe the details of these processes. Such systems as described in these patents have been further defined through the use of any of a large number of specific surfactant types which increase the efficiency of the emulsification process. U.S. Pat. Nos. 4,108,193 and 4,249,554 are illustrative of these refined processes.
The major difficulty with these emulsification processes is that mixing of the aqueous surfactant solution with the heavy, viscous crude is often incomplete with the action of merely a reciprocating pump. This problem was addressed in the aforementioned U.S. Pat. No. 3,380,531 by utilizing the disclosed surfactant and water solution as a power fluid for operating a downhole hydraulic piston pump and exhausting the used power fluid into a mixing chamber located upstream in the flow path for the crude as it approached the reciprocating pump. Such pre-mixing increased the efficiency of the crude oil emulsification to some degree.
Jet-action pumps have been used for producing water and/or oil from subterranean formations. U.S. Pat. No. 4,135,861 describes one form of such a jet pump. A typical jet pump is manufactured by KOBE Inc. and is generally described in their Bulletin 200-06. In the operation of a jet pump, a power fluid is jetted through a nozzle in the flow path of a well fluid. The well fluid is entrained in the jet stream and thereby powered to the surface. Such jet pumps offer many advantages in that they have no moving parts thereby simplifying maintenance; they can be utilized with existing tubing with setting and retrieval being accomplished by standard wire line running and retrieving tools. Previously, however, such jet pumps have never been successfully employed in producing heavy, viscous crudes. The primary difficulty being cavitation of well gases in the throat area of the pump adjacent the high pressure power fluid jet. Such cavitation is apparently the result of the slow movement of the heavy, viscous crude into the throat area. The result of such cavitation is severe erosion of the pump throat within a matter of hours following start-up of the jet pump.